The invention concerns an ignition unit, in particular for an air bag gas generator, having a chamber in which an ignition element and an ignition charge ignitable by it are arranged, with the chamber having at least one opening which is closed and which opens when the ignition charge is ignited for the emergence of the ignition gases from the chamber.
An ignition unit of this kind is known from U.S. patent Ser. No. 4 437 681. The ignition unit is provided with a cylindrical chamber in which a electrically controllable ignition element and an ignition charge ignitable by it are accommodated. The cylinder wall of the chamber is provided with several openings which are closed by a foil or the like. The chamber is arranged in the housing of a gas generator and is surrounded in the latter by the gas-developing material (the pressure-gas-producing charge or the powder bed). As soon as the ignition charge is ignited by the ignition element, the openings open as a consequence of the pressure increase within the chamber and the hot gases arising with the ignition, so that the gases or the flame reach the pressure-gas-producing charge, which is ignited, via the openings. In practice it is not guaranteed that the openings of the chamber are all opened at the same time. Rather it happens that the foil is destroyed first of all in the region of a few openings. Due to the release of pressure occurring therewith, the remaining openings only open at a later point in time or possibly not at all. In this way the required even ignition of the pressure-gas-producing charge is not guaranteed.